This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Automatic Fine Tuning Apparatus In Digital Television Receiver earlier filed in the Korean Industrial Property Office on Dec. 28, 1998, and there duly assigned Serial No. 98-59416 by that Office, a certified copy of which application is attached hereto.
1. Field of the Invention
The present invention relates to a digital television reception and receivers, and, more particularly, to an automatic fine tuning process and apparatus for a digital television receiver.
2. Description of the Related Art
In a digital television broadcast, signals transmitted from a broadcast station to a television receiver as well as the signals within a television receiver are all digital signals, so that more distinct pictures and clearer sounds are provided than those in an analog television broadcast. Digital television receivers provide images of eighteen formats, the receivers ranging from a standard television (SDTV) receiver having a 640xc3x97480 resolution, the same as that of an existing analog NTSC television receiver, to a high definition television (HDTV) receiver having a 1920xc3x971080 resolution, which is seven times larger than that of the SDTV receiver. Digital television receivers vividly reproduce clear stereophonic sounds that exceed those reproduced from compact disks (CD), by adopting a Dolby AC-3 system. Also, digital television receivers use a technique of compressing data by a ratio of 50 to 1 or more, so that the number of channels broadcast by a broadcast station is substantially increased in comparison to the number of channels broadcast by a SDTV broadcast station. Moreover, digital television receivers can achieve interactive transmission, thus providing totally different services in addition to those provided by existing analog television receivers.
An exemplary digital television receiver may be constructed with a tuner feeding an intermediate frequency module. The tuner tunes to one radio frequency channel among the several broadcast signals received via an antenna, under the control of a microprocessor. An intermediate frequency stage module receives an IF signal from the tuner and converts that signal into a baseband signal while a channel decoder produces a data bitstream by decoding the baseband signal output from the intermediate frequency stage module. A TS decoder then separates audio data. video data and additional data from the data bitstream output by the channel decoder.
Digital television receivers receives the various radio frequency signals either through the atmosphere or via a cable like an analog signal broadcast. A radio frequency tuner that is first tuned under the control of a microprocessor exhibits a frequency deviation from its regular frequency band as it passes through several intermediate apparatuses. Accordingly, an automatic fine tuning (AFT) apparatus is required to finely control the RF frequency. We have noticed however, that with conventional automatic fine tuning stages, a channel decoder is able to control variation of the frequency by the second local oscillator to within a range of about xc2x1250 khz. This unfortunately, is, in our opinion, unacceptable because we have found that fine tuning of an error value outside of this restricted control range is not feasible.
It is therefore, one object of the present invention to provide an improved automatic fine tuning process and circuit.
It is another object to provide an automatic fine tuning apparatus capable of fine tuning an error value free a restriction on a predetermined range of frequency.
It is still another object to provide an automatic fine tuning process and circuit able to provide a digital receiver with fine tuning of broadcast signals over a wider range of frequency deviations.
Accordingly, to achieve these and other objects, there is provided a fine tuning apparatus in a digital television receiver with a tuner including first and second local oscillators; a channel decoder outputting an error value with respect to the frequency deviation of an RF signal, which is tuned by the tuner, from the expected baseband signal; and a microprocessor receiving an error value output from the channel decoder and controlling the second local oscillator in the tuner to reduce the error value.